The present invention relates to a power transmission apparatus for transmitting power by utilizing kinetic energy of a fluid, such as a torque converter, a fluid coupling, or the like.
Heretofore, there has been known a power transmission apparatus such as a fluid coupling and a torque converter having a pump impeller coupled to a drive shaft (input shaft) and a turbine impeller coupled to a driven shaft (output shaft) for transmitting power from the drive shaft to the driven shaft through a fluid filled in a casing.
This power transmission apparatus is advantageous in that since it uses oil as a working fluid for power transmission and also uses oil to lubricate bearings thereof, a shaft sealing device is not required between a power transmission section and bearings of the transmission apparatus. However, management of oil is troublesome at the time of overhaul, and treatment of waste oil is problematic from the viewpoint of environmental issue.
Although there is known a power transmission apparatus in which water is used as a working fluid, in this case also, oil or grease is used to lubricate bearings of the transmission apparatus, and hence a shaft seal device is required to be provided between a power transmission section and the bearings of the transmission apparatus, thus making the power transmission apparatus complex in structure.
If a scoop tube is used for speed control in a variable-speed fluid coupling which is one type of power transmission apparatus, then the scoop tube is controlled by a motor servo system, a pneumatic servo system, or a hydraulic servo system.
If water that is inexpensive and can easily be maintained and managed is used as a working fluid for power transmission, then there is a demand for using water to lubricate the bearings of the power transmission apparatus and to operate a servo mechanism for speed control for thereby making the power transmission apparatus structurally simple. In this case, it is a subject to use radial bearings and thrust bearings that can be lubricated by water, and a hydraulic servo mechanism in the power transmission apparatus.
The present invention has been made in view of the foregoing circumstances. It is therefore an object of the present invention to provide a power transmission apparatus which can use water as a working fluid for power transmission and also can use water to lubricate bearings and operate a speed-control servo mechanism.
In order to achieve the above object, there is provided a power transmission apparatus for taking out kinetic energy given to a fluid for power transmission by a prime mover as rotational power, characterized in that water is used as the fluid for power transmission and a lubricating fluid for bearings in the power transmission apparatus.
According to the present invention, the power transmission apparatus has radial bearings comprising sleeve bearings and thrust bearings comprising spiral hydrodynamic bearings, and these radial and thrust bearings can be lubricated by water. A control equipment also has such a structure that water can be used by using a hydraulic servo mechanism or the like.
By replacing oil with water as a working fluid for power transmission and also a lubricating fluid for the bearings in the power transmission apparatus, the following advantages can be obtained:
(1) A conventional shaft sealing structure provided at each of the opposite ends of the shaft in a variable-speed fluid coupling is shown in FIG. 7 of the accompanying drawings, and a shaft sealing structure according to the present invention is shown in FIG. 8 of the accompanying drawings. As shown in FIGS. 7 and 8, whereas a dual labyrinth structure is employed on each of the opposite ends of an input shaft and an output shaft in the conventional shaft sealing structure, a single labyrinth structure is employed on each of the opposite ends of an input shaft and an output shaft according to the present invention.
As shown in FIG. 7, in the conventional shaft sealing structure, two labyrinth structures L1 and L2 are disposed on each shaft end of the input shaft 7 (or the output shaft 16), and a centrifugal leakage water discharging mechanism 50 is disposed between the two labyrinth structures L1 and L2. With this arrangement, a fluid (oil) that has leaked from the first labyrinth structure L1 is trapped by the centrifugal leakage water discharging mechanism 50. Even if the fluid leaks from the centrifugal leakage water discharging mechanism 50, the fluid is prevented from further leaking out by the second labyrinth structure L2.
According to the present invention, only the single labyrinth structure L on each shaft end of the input shaft 7 (or the output shaft 16) is enough to prevent the fluid from leaking out. Even if the fluid leaks from the labyrinth structure L, it has no adverse effect on the environment because it is water.
(2) If the fluid is oil, then the temperature of the fluid increases as the power transmission apparatus operates, and the fluid is turned into minute particles or a mist, and is atomized. Therefore, the power transmission apparatus has an oil mist separator.
If the fluid is water, then even when it is turned into a mist, it has no adverse effect on the environment at all. Therefore, the power transmission apparatus is not required to have an oil mist separator and an air breather which would normally be needed.